It’s likely that you’ve heard by now. There is going to be a total solar eclipse on August 21st, 2017. Maybe you know just how big a deal that is. If not, know, it is a big deal. This is my log of planning for the eclipse.
It’s not every century that a total solar eclipse crosses the United States. There has never been a mainland US crossing total solar eclipse in my lifetime and there have only been a few total solar eclipses in the past century that touched the continent at all.
This is the first total eclipse (the total part is special, more below) in living memory to march straight across the continental US. I’m planning to see it and so should you.
If you are like me, and most people alive, this will be your first total eclipse. That means, it is tough to plan for. Luckily, in the information age, information is easy to come by. I’ve been tunneling through sites and planning. This blog post represents the summary of my planning for my own eclipse trip. I plan on photographing the eclipse in many ways and also enjoying the experience.
Read on to get a start at planning your own eclipse viewing.
Partial vs Annular vs Total Eclipses
If your like me, you probably thought that a total solar eclipse was any eclipse where the moon ended up right in front of the sun. That isn’t the case. There are three types of solar eclipses. The first isn’t that rare. It is the partial eclipse. The moon passes over the sun, but the alignment isn’t perfect. The moon never completely covers the sun or is directly over it. It only blocks a semicircle of it. Every annular and total eclipse has a partial eclipse on the edges.
Annular and total both involve the moon passing directly over the sun in the sky. The difference has to do with the apparent size of the moon relative to the sun.
All that hype about “super moons” has to do with the eccentricity of the moons orbit. Sometimes it is a little closer and other times farther away. When the moon is at its closest during a full moon, you get a “super moon” when the moon is slightly larger in the sky.
What happens when the moon is at its closest during new moon? Usually not much. The moon is up during the day (that is what new moon is) and we hardly notice it, big or small. However, when the sun and moon and earth all align, and you stand in the right place on earth, you get to see a total solar eclipse.
That tiny size difference in the moon’s apparent size makes all the difference in the world. When the moon is at it’s farthest, or even middle distance, it is very slightly smaller in our sky than the sun. That means, even when perfectly aligned a tiny bit of the sun is peaking out around the edge of the moon. You do not get a total eclipse, but an annular eclipse.
However, when the moon is nearest the earth it covers the sun totally. That is a total eclipse, and that is what we are getting on August 21st, 2017.
NASA’s 2017 Eclipse site goes into WAY more technical detail if you want to dig in. There are also some great references on youtube too. I like Smarter Every Day‘s video about the subject with one of the worlds most passionate eclipse chasers.
Getting Under the Eclipse
If you want to see the total eclipse (and you should), you will likely have to travel some. The path of totality is about 100km wide and cuts across the center of the US from west to east (you read that right, it has to do with the relative motion of the moon and sun).
If you are outside this 100km narrow strip, you will see a partial solar eclipse. The sun will always be peaking around one side of the moon. A partial solar eclipse will be visible from anywhere in the continental US, but that isn’t the real show. The real once in a lifetime event occurs under the track of totality. The closer you are to the center, the better it will be. Planning for the eclipse means planning to be in the path of totality.
There are many sources for information on the path of the eclipse. One of my favorites is this interactive google map version(visible below in the iframe) by Xavier M. Jubier. Click anywhere on the map and it will tell you about the various contact times (C1 through C4 – more on these in a moment) as well as giving you a preview of the maximum eclipse from anywhere it crosses. It starts out in satellite mode, but you can switch to street view which makes for easy planning.
Eclipse2017.org has a great rundown of locations to see the eclipse from (broken down state by state) as well as a preflight checklist for the days leading up to the eclipse.
In case you’re wondering, I’ll be watching the eclipse (weather permitting) from Grand Tetons National Park or somewhere in the Jackson Hole area. And weather not permitting, somewhere east or west as far as I can get.
Eclipses have 5 major time checkpoints: C1, C2, MAX, C3 and C4.
C1 is when the edge of the moon first “touches” the edge of the sun. This is the start of the eclipse. For the next hour the moon will slowly be overtaken by the sun. It will block out more and more of its disk.
C2 is when the moon is fully in front of the sun, when the moons trailing edge touches the leading edge of the sun. C2 is when totality begins. With a total eclipse it will get fully dark and you will be able to see the suns corona. Because the actual sun is fully blocked, during totality (between C2 and C3) is the only time you can view the eclipse with your naked eyes.
MAX is the center of totality, when the moon is as close to centered over the sun as it will get for you. If you are directly under the center of totality the moon will be centered exactly over the sun. And, because the moon is slightly apparently larger than the sun for this eclipse, there is some time between C2, Max and C3. Totality (C2 until C3) will last about 2 minutes or a little more for those in the center of the track most places in the US.
Totality is what this eclipse is all about and is the experience most of us have never had and may never have again. It will get dark during the middle of the day. Temperatures will drop noticeably. The corona of the sun may be visible around the moon. This is the only part of the eclipse that you can view with your naked eyes, and only if you are under the path of totality.
C3 is when the leading edge of the moon touches the trailing edges of the sun, and marks the end of totality. For the next hour the eclipse will diminish until finally C4 is reached when the trailing edge of the moon departs the trailing edge of the sun.
C2 and C3 will be accompanied by visual effects. For example C2 and C3 may present something called Baily’s Beads when the sun peaks through valleys on the moon but is still mostly blocked by the moon. The moon will appear to have a partial shining necklace of beads for a few seconds.
Check out Foxwood Astronomy‘s Eclipse Timer app for Android and iOS. It will give you exact contact times for any location you choose, including your current location. It will also give you very persistent voice prompting at each stage of the eclipse. Just remember that if you load a demo eclipse, the next time the clock reaching eclipse time your phone will start to loudly tell you about it!
My contact times in Grand Teton on the path of totality are C1 = 11:16:50, C2 = 12:34:57, Max = 12:36:07, C3 = 12:37:17 and C4 = 14:00:29.
Photographing (and viewing) the Eclipse
First, full disclosure: this is my first total solar eclipse (as I’ve said above). This article represents a log of my own research and planning, and also my experience photographing the sun. I link the things I am referencing and I hope you find the aggregation helpful, and maybe my interpretation also.
First: Don’t Set Your Camera (or Eyes) on Fire
NEVER look directly at the sun with your naked eyes.
NEVER look at the sun through an unprotected optics system (camera, telescope, binoculars).
It is important to understand that looking at the sun with your naked eyes can blind you. When you put a system of lenses and mirrors designed to gather more light and magnify things in front of your eyes, it can blind your almost instantly.
The sun can damage your eyes instantly through a lens and it can also destroy the sensor in your camera… Remember using a magnifying glass to set things on fire? A modern telephoto lens gathers way more light and focuses it better than a cheap magnifying lens.
If you are shooting with a 70-200 f/2.8, the front element has an area of approximately 18,625 mm-squared. It is gathering the solar energy from that entire area and focusing it into an image of the sun and focusing it onto an area 5% the width of the sensor (see below for the source of this figure), or about 10 mm-squared. That is a 1862x as much energy as the sun shining directly on the senor… That is a lot of energy.
A camera probably won’t be damaged instantly, but things will start to heat up. Heat is not good for either moving parts or electronics. Both you and your camera need the right protection.
The Right Eye Protection for your Camera
What is that right protection? User eclipse glasses for your eyes and solar film for your camera lenses. Both are made from the same material: specially process metalized plastic that looks like a silver Mylar survival blanket. Get the real stuff. Survival blankets and other Mylar products are not designed to use as eye protection and often have inconsistent coating and pin holes, all of which can lead to blindness, damaged equipment or just sup-optimal photos. You can also purchase pre-made lens and telescope filters. I choose to make my own.
The solar film and the glasses block most of the incoming light and allows only a tiny fraction of visible light through. When you are looking at the sun, that is more than enough light getting through.
During totality, you can remove both your and your cameras eye protection. It will get much darker (more on this in the exposure section below). Just remember to put them both back on when totality ends.
The sun and moon are both about .5 degrees across in the sky. If you know your lenses horizontal field of view (usually available in the tech specs on the manufacturers site) you can easily determine how large the eclipse will be in your frame.
Here is an example. My Nikon 200-500mm lens, at 500mm on a full frame camera (35mm wide sensor) has a horizontal field of view of about 5 degress. The sun will be 1/10th the width of the frame (12% to be exact). Nikonian has a nice table of FOV for various focus lengths and crops.
Here are some common focus lengths and the relative size of the sun to the frame width.
|Focus Length||Full Frame||DX, APS-C||Micro 4/3|
|15mm||0.5% width||.75% width||1% width|
|35mm||0.92% width||1.4% width||1.8% width|
|100mm||2.5% width||3.7% width||4.9% width|
|200mm||4.9% width||7.3% width||9.7% width|
|300mm||7.2% width||10% width||14% width|
|400mm||9.6% width||14% width||19% width|
|500mm||12% width||18% width||24% width|
|600mm||14% width||22% width||29% width|
|800mm||19% width||29% width||38% width|
|1200mm||29% width||44% width||59% width|
If you shoot with a full frame camera that produce 4000 pixel wide files using a 200mm lens, the sun will be 196 pixels across.
0.049 * 4000 pixels = 196 pixels
To determine the size of the sun in your frame multiply the width of your images in pixels times the % width from the table above. Remember to convert to decimal from % so that 4.9% become 0.049.
What this table should make clear is that you need a pretty long lens to capture decent size images of the sun or moon. You can make wider field images (landscapes) but the sun and eclipse will be much smaller in the frame.
Exposure Before and After Totality
This is a time for full manual control: manual focus, manual exposure and manual ISO. The camera will not understand what you want so don’t risk it being dimwitted at a once in a lifetime event.
Up until totality begins at C2 and again after totality from C3 on, you are basically photographing the naked sun, all be it with a larger and larger chunk taken out. Things will be consistent. You can figure out your settings any clear day with your solar filter and lens of choice. They will be the same for the day of the eclipse. The sun is the sun.
You should be targeting your exposure so the sun is in the middle right of the histogram with no data clipped off on the highlights. With modern cameras you can actually pull out things like sunspots and surface variations if you expose the sun properly. This will leave everything else (background sky) black.
The settings I find work on my setup using solar film are ISO200, f/8, 1/1000s. Your settings may vary… Test!
Exposure During Totality
This is the hard part of planning for the eclipse. It is the part of the event that we can’t test ahead of time. Luckily, this is not the first eclipse in modern times and the internet is a great source of information. For a technical discussion of exposure, see the MrEclipse site. It dates to the film days when you couldn’t guess and check. He works through the math.
Various sources have suggested that the same exposure settings will roughly work for before totality and during totality if you remove the solar film. This seems logical as a starting point since the sun’s corona, the only part visible during totality, is about 1/1,000,000 dimmer than the photo-sphere that is covered by the moon.
A 1/1,000,000 drop in brightness is 20 stops difference for those counting. My solar film reduces the light by about 16 stops. These are close, but not the same. To maintain the exact same exposure, I would need to brighten my exposure 4 stops during totality. With modern digital cameras 4 stops is not to bad to “fix” in post when shooting raw and if you select your per-totality exposure to be on the bright side, the middle right of the histogram as noted above.
You can also just reach over and adjust your exposure as the eclipse happens and verify it on live view or on an image review.
Checking Your Solar Films Stopping Power
The solar film I have stops about 16 stops of light. I know that because I tested it.
You can determine the number of stops yours blocks ahead of time with a simple test. Go outside and find a very bright scene that you can photograph with your unprotected camera. I used the bright blue sky. Do not photography the sun since you will need to take photos of it with and without the solar film.
First, make an exposure without the solar film at your lowest ISO, with your aperture stopped all the way down to it’s darkest. Select a shutter speed so your light meter reads exactly in the center. For me this was ISO64, f/22 and 1/20s.
Now, install the solar film in front of the lens and begin adjusting your settings, starting with ISO, then aperture and finally shutter speed until the light meter reads in the center. This will be a big adjustment.
Take a shot and check the histogram. It will probably be pretty underexposed… The meter got it wrong because it isn’t seeing the same light spectrum as the sensor. The solar film blocks different frequencies of light different amounts. Adjust the exposure and take test shots until the histograms for the photo roughly match the unprotected test shot. My settings ended up being ISO12800, f/2.8, 1/3s.
Comparing the settings from these two test shots with the same exposure value, you can count the stops difference. Simply count the number of stops between each settings and add them up. This is how many stops of light your solar film blocks. In my case, it is about 16 stops.
|Without Solar Film||64||22||1/20s|
|With Solar Film||12800||2.8||1/3s|
|Stops Difference||7 2/3||6||2 2/3||16 1/3 Stops Total|
Combined with the knowledge that the corona is 20 stops dimmer than the photosphere (the sun we normally see), you can determine how much exposure shift you will need with your solar film when totality occurs.
Focus is pretty simple. The sun is at infinity. Some autofocus systems may be able to grab focus on the sun through the solar film. If so, you can focus and then switch to manual focus on your lens or body. Just be careful not to bump the focus ring at any point.
If your camera won’t grab focus on the sun through the solar film, with the solar film on, switch to live view with the camera in manual focus mode. Zoom in on the sun in live view and gently manually dial in the focus until the edge of the sun is tack sharp.
Modern lenses do NOT have infinity stops. Therefore, you can’t simply crank the focus all the way out to infinity. The image will be out of focus, especially on a telephoto lens.
A Moving Target
The sun is a moving target. It shifts about one quarter degree (.25 degrees) per minute (360 degrees per 24 hours). Over the course of totality where I plan to watch, 2 minutes and 20 seconds, that equates to .58 degrees of movement across the sky. When you add in the width of the sun (you want it fully in frame the entire time), you get 1.08 degrees of total movement just during totality.
If I shoot or film for 3 minutes before and after totality, for a total of 8m 20s, then the sun will cover 2.08 degrees plus the sun’s .5 degree width, or 2.58 degrees.
2.58 degrees is 5 solar widths: .5 degrees = 1 sun width
Looking at the lens chart above, you can see that unless you have a pretty serious lens, you can take photos or video of the entire totality without moving the camera. Continuing the example, if I am shooting with my 500m lens on a full 35mm frame, and I take stills or video for 8m 20s, the sun will cross 60% of the frame during that time.
5 solar widths @ 500mm = 5 * 12% = 60%
If all of that sounds to complicated, check out Smarter Every Day 2’s interview with Gordon Telepun of Foxwood Astronomy about planning for the eclipse. He outlines what he calls the “drift” method. It describes how to figure this stuff out through trial and error before the eclipse without math.
Tracking the Sun
If you are shooting with an extremely long lens (or telescope), or if you just want to keep the sun centered in your frame, or if you would like to photograph the entire eclipse including the partial eclipse run-up to totality (about 3 hours total), you need to use a tracking system. An equatorial mount is the option of choice since it naturally follows objects “moving” around the planet. I’m working on one for myself now, but haven’t finished building it, so I have nothing to share…. yet.
If you want to track the sun, it’s time to go down the rabbit hole on your own. Come back and share what you find with us, and your images!
Equipment for the Eclipse
I haven’t really touched on equipment other than lens focus length. If you are wondering what it takes to photograph this type of event, it is actually pretty simple.
You need a good tripod. With a tripod you can aim the camera and leave it alone.
You need a camera with manual mode. Because the sun is bright (reference needed), just about any interchangeable lens camera (or even fixed lens if it has enough zoom) will work. Normally when I’m photographing stars it is at night and you need the right camera body, but in this case, nothing very special is needed.
You need a long lens if you want to make the sun big in your picture since it is actually pretty small in the sky.
And finally, you might want a remote release, and in particular a programmable intervalometer so you can have the camera take photos continually without your intervention.
You can add more if you want, but that is all that is required.
Planning for the Eclipse
If you are still with me, thank you. I know this was a long dense post. As you can see, you can do a lot of planning. If that is to much for you, just go see the eclipse and don’t worry about photographing it. This might be the single most photographed astronomical event in history, but no photo will capture the feeling of darkness mid day, and of being able to see the corona of the sun.
So, plan your location, make your travel plans and make sure you have at least eye protection. And then go and experience the event.